Exhaust silencers

ABSTRACT

An exhaust silencer comprises a body which includes inner, intermediate and outer coaxial tubes. The outlet is formed as a slot and immediately upstream of the outlet in the direction of gas flow is a passage between the intermediate and outer tubes, the height of the passage being such as to attenuate the sound of the gas flowing through the passage. Between the inner and intermediate tubes is one or more resonator chambers and the exhaust gas flows through the inner tube and the passage in one direction and through the chambers in the opposite direction.

United States Patent [191 Roe et al.

[ EXHAUST SILENCERS [75] Inventors: Geoffrey Ernest Roe, Bramhall;

John Edward Favill, Dudley, both of England [73] Assignee: NortonViIIiers Limited,

Staffordshire, England [22] Filed: Oct. 29, 1973 [21] App]. No.: 410,409

[30] Foreign Application Priority Data Apr. 18. 1973 United Kingdom l.18675/73 [52] US. Cl. 181/53 [5i] Int. Cl. F0ln 1/08 [58] Field ofSearch 181/53-57 [56] References Cited UNITED STATES PATENTS 674,2IO5/1901 Loomis I8l/57 X 1,598,578 Maxim l8l/S3 June 10, 1975 3073.684l/l963 Williams l8l/55 UX FOREIGN PATENTS OR APPLICATIONS 781,087 5/[935France l8I/53 Primary ExaminerRichard B. Wilkinson AssistantExaminer-John F. Gonzales Attorney, Agent, or FirmSpencer & Kaye [57]ABSTRACT An exhaust silencer comprises a body which includes inner,intermediate and outer coaxial tubes. The outlet is formed as a slot andimmediately upstream of the outlet in the direction of gas flow is apassage between the intermediate and outer tubes, the height of thepassage being such as to attenuate the sound of the gas flowing throughthe passage. Between the inner and intermediate tubes is one or moreresonator chambers and the exhaust gas flows through the inner tube andthe passage in one direction and through the chambers in the oppositedirection.

4 Claims, 5 Drawing Figures SHEET PATENTEDJUH I 0 I975 FIGS EXHAUSTSILENCERS This invention relates to exhaust silencers for use inassociation with internal combustion engines to reduce the noise levelof the exhaust without effecting the power output of the engine to anunacceptable extent.

The exhaust noise from an internal combustion engine encompasses a bandof frequencies and the noise level normally peaks over a compact rangeof frequencies within the band. Silencers are designed to attenuate thenoise within the range of frequences where the noise peaks, thus toreduce the overall level of the noise.

It is known to employ for this purpose a number of resonators oracoustic filters which are tuned to respond to different frequences inthe range. Standing waves are thus formed and the supply of energyrequired to keep these standing waves in existence attenuates the noiselevel within said range and thus the peak noise level of the exhaust.

The object of the invention is to provide an improved silencer usingresonating chambers.

According to the invention we provide an exhaust silencer comprising: abody which includes inner, intermediate and outer co-axial tubes; anexhaust gas inlet at one end ofthe body and in one end of the innertube; an exit opening at the other end of the inner tube; an outlet atthe other end of the body in the form ofa slot; a passage between theintermediate and outer tubes immediately upstream of said slot in thedirection of flow of the exhaust gas, the passage having an inlet andter minating in the slot; the walls of the passage being imperforate andspaced apart by a distance such that the height of the passage betweenthe walls is such as to cause attenuation of the noise of gas flowingthrough the passage while the area of the slot and of the cross sectionof the passage transverse to the direction of .low of gas therethroughis at least as great as the crosssectional area of the inlet transverseto the general direction of flow of exhaust gases through the inlet; thepassage having a length equal to at least times the height of the slot;there being no part of the flow path of the gas between the inlet andthe outletwhich has a cross-sectional area perpendicular to the generaldirection of gas flow which is less than said cross-sectional area ofthe inlet; and there being one or more chambers between the exit openingof the inner tube and the inlet to the passage and arranged so that thedirection of flow of exhaust gases through the chamber or chambers is ina direction generally opposite to the direction of flow of exhaust gasesthrough the inner tube and the passage.

We have found that by having an outlet in the form of a slot and apassage upstream of the slot and having imperforate walls, the noiselevel of the exhaust is attenuated to a greater extent than in exhaustsilencers using resonators or acoustic filters as heretofore provided.We do not wish to be bound by an explanation as to why this attenuationis obtained but we believe that it is obtained because of interferenceand damping which takes place between the pressure waves in the gas asthe waves travel along the passage to the outlet slot.

The exit opening of the inner tube may lead to a diffuser from which thegas passes to the chamber or chambers between the inner and intermediatetubes.

The slot can be continuous, for example. circular, oval, rectangular orof sinuous shape. Alternatively, the slot can be finite and may bestraight or arcuate. In any event, the slot is preferably of a constantwidth along its length. The cross-sectional shape (and hence the height)of the passage is preferably the same as that of the slot and thepassage is preferably of a length greater than fifty times the height ofthe slot.

The silencer may include, between the inner and intermediate tubes, anumber of resonator chambers arranged in series and tuned to differentfrequencies within the frequency band of the exhaust noise to besilenced. The chambers may be placed in communication by a number oftuned pipes and spaced apart around the inner tube.

In designing the silencer we have found that it is desirable that theheight of the slot and of the passage shall not be greater thanone-tenth of the shortest wave length of the sound to be attenuated andshall not be less than one-tenth of a quarter of such shortest wavelength. The height of the passage is the dimension thereof correspondingto the height of the slot.

It is preferred that the slot be in the form of a sharpedged orifice butthis is not essential.

Two embodiments of the invention will now be described in detail by wayof example with reference to the accompanying drawings in which:

FIG. 1 is a longitudinal section through a silencer constituting a firstembodiment of the invention;

FIG. 2 is a section on the line 22 of FIG. 1;

FIG. 3 is a section on the line 3-3 of FIG. 1;

FIG. 4 is a section on the line 44 of FIG. I and FIG. 5 is adiagrammatic cross section through a second embodiment of the invention.

Referring now to FIGS. 1 to 4 of the drawings, the silencer there showncomprises an inner tube 10 which at the inlet end, the left hand end inFIG. I, is surrounded by a front tube 11 which is adapted to beconnected to the exhaust pipe of an engine. At its right hand end theinner tube 10 has an exit opening which leads to a diffuser indicatedgenerally at 12 and connected to the tube 10. The diffuser has acylindrical part 13 which fits over the right hand end of the inner tube10, a frusto-conical part I4, a cylindrical part 15 of greatercross-sectional area than the part 13 and an end plate 16. The end plate16 is imperforate but the cylindrical portion 15 is provided with aplurality of slots some of which are shown at 17. The inner tube 10 andthe diffuser 12 are so dimensioned that the distance between the endplate 16 and the exhaust ports of the engine is the optimum distance forthe generation of engine power.

Surrounding the inner tube 10 is an intermediate tube 18 and surroundingthe tube 18 is an outer tube 19. The tubes l0, l8 and 19 are coaxial andare cylindrical as will be clear from FIG. 2. Two support rings 20 areinterposed between the tubes 18 and 19 and are spaced apartlongitudinally of the tubes. As shown in FIG. 2, each support ring hasthree outer portions 21 which engage the outer tube 19 and three innerportions 22 which engage the intermediate tube 18. It will be seen thatthe support rings locate the intermediate tube within the outer tubewithout substantially obstructing the cross-sectional area of an annularoutlet passage 23 between the tubes 18 and 19 and which has an entranceat the left hand end of the intermediate tube 18.

The right hand end of the tube 18 is closed by an end plate indicatedgenerally at 24. This end plate has a circular portion 25 opposite tothe end plate 16, a diverging wall portion 26 and a cylindrical portion27 which flts within, and is secured to, the tube 18. The outlet fromthe outlet passage 23 is a slot indicated at 28 and it will be seen thatit is formed between the opposed rear ends of the outer tube 19 and theintermediate tube 18. The length of the outlet passage 23 is thus fromthe entrance at the left hand end of the tube 18 to the slot 28.

The left hand end of the outer tube 19 is connected to the largerdiameter end 29 of a front cone 30, the smaller diameter end 31 thereofbeing connected to the front tube 11.

An annular front plate 32 surrounds the tube and is secured thereto by aflange 33. The front plate 32 is located adjacent the left hand end ofthe outer tube 19 and is provided with a number of equi-angularly spacedapertures 34, some of which are seen in FIG. 4.

Between the inner tube 10 and the intermediate tube 18 are mounted frontand rear baffles. The front baffle is indicated generally at 35 and is aring of substantially Z cross section having an inner flange 36 weldedto the tube 10 and an outer flange 36a welded to the tube 18. The bafflecarries six pipes 37 which, as shown in FIG. 2, are equi-angularlyspaced around the tube 10. The left hand ends of the tubes 37 aresupported by a flanged ring 38 welded to the tube 10.

in a similar manner, the rear baffle 39 is an annular ring of Zcross-section having an inner flange 41 welded to the tube 10 and anouter flange 41a welded to the tube 18. The baffle 40 carries twelvepipes 40 which are equiangularly spaced as shown in FIG. 3. It will benoted that the pipes 40 are shorter and smaller in diameter than thepipes 37.

The baffles 35 and 39 divide the space between the tubes 10 and 18 intotwo chambers 42 and 43. A fur ther chamber 44 is provided within theouter tube 19 to the left or forwardly of the front baffle 45 and a deadair space 45 is provided within the front cone 30 around the tube 10.

Pommels 46 are welded to the outer tube 19 to provide means for mountingthe silencer on a support bracket.

In operation, exhaust gas flows from left to right along the inner tube10. When the gas reaches the diffuser 12 the gas expands and itsvelocity decreases and it passes through the slots 17 into the chamber42. The gas then passes through the pipes 40 into the chamber 43 andthrough the pipes 37 into the chamber 44. The volumes of the chambers42, 43 and 44 and the lengths and diameter of the pipes 37 and 40 arearranged to provide the desired attenuation characteristics for thesilencer. The gas then flows from the chamber 44 along the outletpassage 23 and through the outlet 28. The gas flow is in contact withthe dead air space 45 through the apertures 34 and this gives furtherattenuation. It will be noted that the chamber 44 has a greater volumethan the chamber 43 which has a greater volume than the chamber 42.

The cross-sectional area of the flow path of the gas is not restrictedbetween the entry to the inner tube 10 and the exit from the outlet 28.Preferably the crosssectional area of the outlet is greater than that ofthe inlet and may be 40 percent greater. The outlet 28 is in the form ofa slot which is at the downstream end of the passage 23 whose concentricwalls, provided by the tubes 18 and 19, are imperforate and are aconstant distance apart. The cross-sectional area of the outlet 28 canbe considered to be defined by the inner surface of the outer tube 19and the outer surface of the inner tube 18 as it has been found that theexhaust gases emerging from the outlet do not follow the angle of thediverging wall portion 26 unless this angle is less than 8. The heightof the passage 23 and slot 28 is the radial distance between the outersurface of the intermediate tube 18 and the inner surface of the outertube 19. The height of the passage is such as to cause attenuation ofthe noise of the exhaust gas flowing through the passage. The passagehas a length equal to approximately times the height of the slot (andalso the height of the passage itself) although for this embodiment itcould be between 50 and 60 times the height of the slot.

Referring now to FIG. 5 this shows another embodiment of the inventionin which the silencer comprises an elongated body 50 comprising an outertube 51 and an intermediate tube 52. The outer tube 51 is longer thanthe inner tube 52 and there is an annular passage 53 between the tubeswhich leads to an annular exit slot 54 similar to the slot 28 in FIG. 1.The passage 53 corresponds to the passage 23 in the first embodiment andis similarly dimensioned to attenuate the noise of the exhaust gasflowing through it. The tube 52 has a closure 55 at the outlet end ofthe silencer and has a perforated plate 56 at its other end.

The inlet end of the silencer is indicated at 57 and comprises a cone 58welded to the outer tube 51 and also to an inner tube 59 which extendsinto the cham ber 60 provided within the tube 52 and is connected at itsend to an apertured diffuser 61 which has a number of apertures 62therein. The length of the passage 53 is at least 15 times the height ofthe outlet slot 54 and there is no restriction to flow between the inletto the tube 59 and the slot 54.

The operation of the silencer of FIG. 5 is as follows. Exhaust gasenters through the tube 59 and flows into the diffuser 61 and fromthence through the apertures 62 into the chamber 60 which acts as aresonator and absorbs sound energy. The gas then flows through apertures63 in the plate 56 into the chamber 64 provided in the outer tube 51 andthis chamber 64 also acts as a resonator absorbing further sound energy.It will be understood that the chambers 60 and 64 are tuned to resonateat different frequencies within the range of frequencies required to beattenuated by the silencer. The gas then flows from the chamber 64 alongthe passage 53 to the outlet slot 54 which is in the form of a sharpedged orifice. The passage 53 which has imperforate walls formed by thetubes 51 and 52 acts in the same manner as the passage 23 of FIGS. 1 to4 and we have found that the inclusion of such a passage improves theperformance of the silencer as compared with those known heretofore.

It is also necessary that there be no restriction in the silencer andtherefore the cross sectional area of the slot such as 28 or 54 must beat least equal to the cross sectional area of the tube 10 or 59respectively. It follows that the cross sectional area transverse to thedirection of flow of the gas through the silencer must not, at anyposition, be less than the cross sectional area of the inlet to thesilencer constituted by the tube 10 or the tube 59.

We claim:

1. An exhaust silencer comprising: a body which includes inner,intermediate and outer co-axial tubes; an exhaust gas inlet at one endof the body and in one end of the inner tube; an exit opening at theother end of the inner tube which is imperforate between its one end andthe exit opening; an outlet at the other end of the body in the form ofa slot; an outlet passage defined between concentric inner and outerwalls provided by the intermediate and outer tubes respectively andbeing located immediately upstream of said slot in the general directionof flow of the exhaust gas, the outlet passage having an entrance at oneend and terminating in the slot at the other end and being arranged sothat all the exhaust gas flows therethrough; said concentric walls ofthe passage being imperforate and spaced apart by a constant distanceover the whole of the overlapping lengths of the intermediate and outertubes; said distance being such that the height of the passage betweenthe walls is such as to cause attentuation of the noise of gas flowingthrough the outlet passage while the area of the slot and of thecross-section of the outlet passage transverse to the general directionof flow of the gas therethrough is at least as great as thecross-sectional area of the inlet transverse to the general direction offlow of exhaust gases through the inlet; the outlet passage having alength between the entrance and the slot equal to at least 50 times theheight of the slot and providing a clear path for gas flow in adirection parallel to the longitudinal axis of the passage between theentrance and the slot; there being no part of the flow path of the gasbetween the inlet and the outlet which has a cross-sectional areatransverse to the general direction of gas flow which is less than saidcross-sectional area of the inlet; there being one or more chambersthrough which the gas flows on emerging from the exit opening of theinner tube and arranged so that the direction of flow of exhaust gasesthrough the chamber or chambers is in a direction generally opposite tothe direction of flow of exhaust gases through the inner tube and thepassage, and there being a further chamber defined between the inner andouter tubes into which the gas flows on emerging from said firstmentioned chamber or chambers, the general direction of flow of gasbeing reversed in said further chamber from the entrance to which thegas passes directly to the entrance to the outlet passage.

2. A silencer according to claim 1 wherein the exit opening of the innertube leads to a diffuser from which the gas passes to the chamber orchambers between the inner and intermediate tubes.

3. A silencer according to claim 1 wherein there is a number of thefirst mentioned chambers between the inner tube and the further chamber,all said chambers acting as resonators, being arranged in series andbeing tuned to different frequencies within the frequency band of theexhaust noise to be silenced.

4. A silencer according to claim 3 wherein adjacent chambers are placedin communication via tuned pipes spaced apart around the inner tube.

1. An exhaust silencer comprising: a body which includes inner,intermediate and outer co-axial tubes; an exhaust gas inlet at one endof the body and in one end of the inner tube; an exit opening at theother end of the inner tube which is imperforate between its one end andthe exit opening; an outlet at the other end of the body in the form ofa slot; an outlet passage defined between concentric inner and outerwalls provided by the intermediate and outer tubes respectively andbeing located immediately upstream of said slot in the general directionof flow of the exhaust gas, the outlet passage having an entrance at oneend and terminating in the slot at the other end and being arranged sothat all the exhaust gas flows therethrough; said concentric walls ofthe passage being imperforate and spaced apart by a constant distanceover the whole of the overlapping lengths of the intermediate and outertubes, said distance being such that the height of the passage betweenthe walls is such as to cause attentuation of the noise of gas flowingthrough the outlet passage while the area of the slot and of thecroSssection of the outlet passage transverse to the general directionof flow of the gas therethrough is at least as great as thecross-sectional area of the inlet transverse to the general direction offlow of exhaust gases through the inlet; the outlet passage having alength between the entrance and the slot equal to at least 50 times theheight of the slot and providing a clear path for gas flow in adirection parallel to the longitudinal axis of the passage between theentrance and the slot; there being no part of the flow path of the gasbetween the inlet and the outlet which has a cross-sectional areatransverse to the general direction of gas flow which is less than saidcrosssectional area of the inlet; there being one or more chambersthrough which the gas flows on emerging from the exit opening of theinner tube and arranged so that the direction of flow of exhaust gasesthrough the chamber or chambers is in a direction generally opposite tothe direction of flow of exhaust gases through the inner tube and thepassage, and there being a further chamber defined between the inner andouter tubes into which the gas flows on emerging from said firstmentioned chamber or chambers, the general direction of flow of gasbeing reversed in said further chamber from the entrance to which thegas passes directly to the entrance to the outlet passage.
 2. A silenceraccording to claim 1 wherein the exit opening of the inner tube leads toa diffuser from which the gas passes to the chamber or chambers betweenthe inner and intermediate tubes.
 3. A silencer according to claim 1wherein there is a number of the first mentioned chambers between theinner tube and the further chamber, all said chambers acting asresonators, being arranged in series and being tuned to differentfrequencies within the frequency band of the exhaust noise to besilenced.
 4. A silencer according to claim 3 wherein adjacent chambersare placed in communication via tuned pipes spaced apart around theinner tube.